Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
848 PM PDT Wed Oct 26 2016
A low will arrive Thursday with subtropical moisture to create a
slight chance of thunderstorms and peak precipitation amounts from
Thursday into Friday. Another low will bring possible precipitation
from Saturday into early next week with temperatures below normal.
Marine inversion was near surface-based at klax early this evening,
while a weak inversion was near 1000 ft at kvbg. No low clouds were
over the coastal waters this evening, with mostly clear skies noted
across the forecast area with just a few hi clouds at times.
Additional hi clouds will move into the area overnight as a storm
system over the E pac will slowly approach the area. A few low
clouds and patchy dense fog may develop over the coastal waters to
some coastal areas late tonight, but overall generally fair skies
should prevail for most of the night across the region.
A deep upper level trof was over the ern pac along 135w this
evening. An upper level low is forecast to develop at the base of
the trof around 35n/134w overnight. This system will track NE thru
Thu night then push into central California on Fri. It's associated surface
low pressure system and cold front will move toward the forecast
area on Thu, then pass thru the region Thu night and Fri morning.
Precip ahead of the main storm system will spread into slo/sba
counties thru the day on Thu, with rain spreading across l.A./Vtu
counties Thu night into Fri morning. There will be enough
instability and cape (around 400-500 j/kg) with the main front Thu
night into Fri morning for a slight chance of thunderstorms as well.
This will be a very warm weather system, with snow levels at or
above the highest peaks.
Precipitable water values will be extremely high for this time of year due to the
subtropical nature of a moisture plume being pulled northward ahead
of the upper trof. Pwats up to 1.80 inches are forecast to move into
the central coast with the front. Highest rainfall rates are
expected to be 0.50 inch or more per hour with the heaviest precip,
especially in any thunderstorms. This will bring the threat of flash
flooding with debris flows in and around recent burn areas. Flash
flood watches for the recent burn areas are in effect, starting Thu
afternoon to Thu evening over slo/sba counties, and late Thu night
for vtu/l.A. Counties. The flash flood watches will be in effect
thru Fri morning.
Rainfall estimates with this storm through Fri morning are for 0.50-
1.00 inch to fall in many areas, but potentially higher where
thunderstorms occur. South-facing foothills and mountains will have
higher totals due to strong orographic lift and the very moist
subtropical airmass with 1.00-2.00 inches. The coastal hills of slo
County will likely have the most rainfall, with 2.00-4.00 inches
Strong southerly winds will also be possible with this storm system
over the mtns of vtu/l.A. Counties, especially Thu night into Fri
morning as the main front passes through. Wind gusts up to 45 mph
can be expected, with wind advisories possible being needed for this
A moist south to southwest flow will persist over swrn California Fri
afternoon thru Sat. This combined with the approach of another upper
level trof on Sat will keep cloudiness and a slight chance of
showers over the forecast area thru the period.
Temps are expected to be several degrees above normal over vtu/l.A.
Counties on Thu, and near normal to slightly above normal for
slo/sba counties. Temps should then be slightly below normal for many
areas Fri, and near normal for the most part on Sat.
***From previous discussion***
Then a second upper level eastern Pacific trough slides across
the northern part of the state on Sunday which would give US
another chance of rain, mostly across northern counties. This
system should be a little cooler and will knock a few degrees off
afternoon high temperatures, especially in the mountains.
High pressure begins to ridge across the region by Halloween with
drier and warmer conditions rebounding across the state. However,
the storm train will continue with another system poised to move
across central and northern California on Tuesday. There are
typical timing and strength issues with medium range models, but
have brought a slight chance of rain into the central coast area
for Tuesday, then dry again by Wednesday. Lower confidence in this
scenario, but the storm next week does not indicate much of an
impact for southwest California.
At 2307z, the marine inversion at klax was at 800 feet deep.
The top of the inversion was at 2000 ft with a temp of 23 deg c.
VFR moderate to hi confidence in the 00z tafs.
Moderate to hi confidence in the 00z tafs. VFR conditions are
forecast at all the airfields tonight. However, there is a 30
percent chance of low clouds and LIFR cigs at ksbp and ksmx late
tonight into Thu morning. Low clouds and LIFR conditions are
expected to develop at klax and klgb by 13z Thu and persist thru
about 17z, altho there is a 30 percent chance these low clouds may
not develop. MVFR cigs with rain should move into kprb, ksbp and
ksmx for Thu afternoon. Otherwise, VFR conditions should prevail at
the airfields on Thu.
Klax...moderate to hi confidence overall in the 00z taf. VFR
conditions are expected at the airfield thru Thu evening, except for
a period of IFR conditions with low clouds from about 13z to 17z,
and MVFR vsbys 17z to 20z. However, there is a 30 percent chance the
low clouds may not develop., And the timing of the development of
any low clouds could be off +/- an hour or so.
Kbur...generally hi confidence in the 00z taf with VFR conditions
expected at the airfield thru Thu afternoon.
There is moderate confidence that winds and seas will likely
remain below Small Craft Advisory levels through Saturday. However, brief localized
small craft wind gusts are possible along and just ahead of a cold
front moving through the waters from west to east late Thursday
into Friday. Patchy dense fog may redevelop tonight and persist
into Thursday morning. Moderate to heavy rain with the slight
chance of thunderstorms is expected along and ahead of a cold
front moving west to east late Thursday into Friday.
A lingering long period south swell originating from Hurricane
Seymour combined with a building long period swell originating
from an elongated low pressure system over the North Pacific may
bring small craft conditions due to hazardous seas as early as
late Saturday and more likely Sunday continuing into Monday
across the outer waters.
California...Flash Flood Watch in effect from Thursday afternoon through
Friday morning for zones 34-35-37. (See laxffalox).
Flash Flood Watch in effect from Thursday evening through
Friday morning for zones 36-39-52-53. (See laxffalox).
Flash Flood Watch in effect from late Thursday night through
Friday morning for zones 40-45-46-54-59-547-548. (See laxffalox).